February 19, 2004

Mussels may lead to safer implants

Medical implants may soon get better at preventing life-threatening clogs and bacterial infections thanks to an unusual coating that is being developed from mussels, according to Northwestern researchers.

Phillip B. Messersmith, assistant professor of biomedical engineering, is lead investigator in the study of the two-sided coating.

photo by Stephen Anzaldi

They have developed a two-sided coating: one side is a sticky glue based on adhesive proteins secreted by mussels, the other is a special repellant. While the sticky side is designed to attach securely to the surface of the implant, the repellant side prevents the build-up of cells and proteins that typically foul implant devices such as cardiac stents, urinary catheters and dialysis tubing. Such contamination can lead to device malfunction, blood clots or fatal bacterial infections, the researchers say.

Their findings, based on laboratory studies, were published in the Journal of the American Chemical Society, a peer-reviewed publication of the American Chemical Society, the world’s largest scientific society.

Medical implant contamination, particularly that caused by bacterial infections, is a major medical challenge today. Although researchers have been developing anti-adhesive coatings and other anti-infective techniques for medical devices for years, no single approach works effectively for all types of implant surfaces, says Phillip B. Messersmith, assistant professor of biomedical engineering, and lead investigator in the study.

“Our goal is to take advantage of the unique ability of mussels to attach to all types of surfaces, including Teflon, in order to develop a compound that will allow us to treat a variety of implant surfaces with a single approach,” Messersmith says. Such a coating would be more versatile and cost-effective than those currently used, he predicts.

The foot of the common mussel (Mytilus edulis) produces a sticky glue that keeps the shelled organism anchored to rocks and other objects, allowing them to withstand the extreme pounding of waves. Chemical analysis of this natural, water-proof glue has shown that the key to its adhesiveness is a unique compound called mussel adhesive protein, which contains a high concentration of an amino acid, DOPA (dihydroxyphenylalanine), which can cling to wet surfaces with extraordinary strength.

While several researchers have focused their attention on developing these mussel adhesive proteins into a type of super-glue, Messersmith reasoned that the same compounds could be used to anchor a repellant component. He decided to attach the sticky DOPA molecule to a well-known repellant molecule, polyethylene glycol (PEG).

The result: A two-sided compound whose sticky side attaches to internal surfaces, but whose nonstick side can resist protein and cell attachment, such as that encountered by implanted medical devices.